In spite of being a rather charming Norman village, that dates way back in time, Giverny owes its fame and popularity to one place and to one brief period of history. However, when this is Monet's garden, who could ask for more?
The whole garden is a total delight - unless you happen to pick a day when the lily-pond is drained for cleaning. Then there's still plenty to see and the admission fee is reduced but - - you could phone first and check.
If you want to know about Giverny, it would be superfluous to try to add anything to an excellent report on this site:
http://www.globosapiens.net/britman-travelogue/Giverny.html
